подскажите чем вызвана ошибка
Jul 19 14:36:03 asterisk[6435]: WARNING[7708]: app_dial.c:2341 in dial_exec_full: Unable to create channel of type 'SIP' (cause 20 - Subscriber absent)
Jul 19 14:36:32 asterisk[6435]: WARNING[7709]: app_dial.c:2341 in dial_exec_full: Unable to create channel of type 'SIP' (cause 20 - Subscriber absent)
Jul 19 14:36:32 asterisk[6435]: WARNING[7709]: app_dial.c:2341 in dial_exec_full: Unable to create channel of type 'SIP' (cause 20 - Subscriber absent)